Electrolytic refining of copperbearing materials



Patented Oct. 24, 1944 UNITED STATES PATENT OFFICE ELECTROLYTIC REFINING OF COPPER- BEARING MATERIALS Sidney A. Corren, Tottenville, Staten Island, N. r.

assignor to Nassau Smelting & Refining Company', Incorporated, New York, N. Y., a corporation of New York No Drawing. Application August 1, 1940, Serial No. 349,244

16 Claims.

This invention relates to the electrolytic refining of copper-bearing materials and more particularly to the refining of material consisting primarily of copper and containing lead and In one process which has been practiced previously, the scrap material is treated in a blast furnace to eliminate the iron andv the resultant molten metal is charged into a converter where substantially all of the zinc only is removed by blowing with air. The metal from the converter is cast into anodes and is electrolyzed for the production of copper in a sulphuric acid electrolyte of relatively low concentration. During the electrolysis most of the metals other than copper, such as lead and $111,216 converted into insolubl compounds, and some of these compounds adhere to the anodes, some remain suspended in the electrolyte and the balance falls the formation of hard slimes on the anodes with somewhat the same results.

Due to the rapid formation of lead sulphate upon the anodes, it has been found necessary to employ low. sulphuric acid concentrations inthe electrolytic baths previously employed. It has i been found that when concentrations of the order of -100 grams per litre of free sulphuric acid are employed th anodes polarize rapidly and the cell is soon rendered inoperative. Consequently, the free sulphuric acid used in these baths is .substantially less than 100 grams per litreland frequently isin the vicinity of 50 grams per litre. Apparently, when small quantities of sulphuric acid are employed the polarization of the anodes is deferred somewhat and the process will operate for a considerable period of time, but only at the sacrifice of efficiency and at higher cost than would be the case if more sulphuric acid could be used. The economic losses resulting from high cell voltages and the necessity of scraping or to the bottom of the electrolytic cell in the form .high cost of the electrolytic refining due to the abnormally high cell voltages necessitated by the low'conductivity of the electrolyte and the fact that the slimes produced tend to interfere with the operation of the electrolytic cell. Copperbearing materials of the type in question invariably contain lead which reacts with the sulphuric acid in the bath to form insoluble lead sulphate in the form of a hard film directly upon the anodes. This film tends to insulate the anodes from the bath, thus increasing the voltage necessary to cause a current to flow therethrough, and in most cases ultimately renders the anodes totally insoluble or, in other words, polarizes the anodes. When the anodes are in this condition, they must be replaced by fresh anodes and the polarized anodes have to be scraped'to remove the slimes or worked up into new anodes. Other working up undissolved anodes, which are caused by these peculiarities of the anode slimes, are obvious.

Among the objects of the present invention are the provision of effective and economical electrolytic methods of refining copper-bearing materials and the elimination of the adverse efiects of anode slimes in processes of this nature.'

A further object of the invention is to provide new and useful electrolytes for use in such electrolytic refining processes.

In accordance with one embodiment of the invention, the material to be refinedis treated in the usual manner to remove the iron and as much zinc as possible without losing substantial quantities of tin andlead. The resulting metal is cast into anodes which are electrolyzed in a copper sulphate-sulphuric acid electrolyte containing an aromatic sulphonic acid radical which will combine with lead to form a lead salt that is soluble in water, in sufiicient quantity to prevent or materially retard the polarization of the anodes by the anode slimes. Preferably, benzene disulphonicacid is employed to supply the aromatic sulphonic acid radical. The electrolyteemployed preferably contains a higher concentration of acid than is customary in the processes of the prior art, thereby decreasing the resistance of the cell and permitting the use of lower voltages than have been employed heretofore. The

anodeslimes produced are worked up in any suitable way to recover. the metallic values contained therein. a

The above described and other objects and the original material.

to an oil fired converter where some silica is tially absent.

features of the invention will be fully apparent from the following detailed description of specific processes and electrolytes embodying the invention.

In carrying out the invention, impure copper bearing materials from any suitable sources are charged into ablast furnace along with limestone and coke and the material is srnelted to eliminate most of the iron in the form of'a slag. The copper-bearing materials charged into the blast furnace may be of. varied types and compositions. The charge may comprise junked electrical apparatus containing brass, bronze, iron, copper, lead, solder, german silver, chromium, nickel, aluminum, zinc, and variousnon-metallic materials, principally insulating materials. The charge may also include or consist of other copper-bearing scraps and junked materials, machine shop sweepings, and miscellaneous refinery and foundry scraps, slags, ashes, etc. Typical raw materials suitable for use in this process might contain about to 60% copper, 0.5 to" tin, 0.5 to 20% lead, and the balance principally iron, zinc, and non-metallic materials.

metallic impurities, such as chromium and aluminum, will be substantially eliminated in the slag. Other metallic impurities, for example, nickel, will enter the pig metal produced in the blast furnace, but they will not interfere with the subsequent operations.

The pig metal taken from the blast furnace contains practically all of the copper, tin and lead and a substantial part of the zinc found in This metal is transferred anodes which consist principally of copper, tin

and lead, but which may contain minor quantities of such metals as zinc, antimony, nickel and iron. Anodes produced by treating iunked telephone equipment might contain approximately 70 to 95% copper, 0.5 to 15% tin, 0.5 to 15% lead, and the remainder a mixture of small amounts of other metals. Typical anodes obtained from materials of the type referred to comprised substantially 86 to 90% copper, 3.5 to 6% tin, 5 to 8% lead and about 1% zinc, together with a small amount of other metals, such as antimony, nickel and iron.

It will, of course, be obvious that if the original material to be refined is substantially free from either iron or zinc, the step employing the blast furnace or the converter will be omitted, and likewise that both of these operations will be unnecessary if both iron and zinc. are substan- Any other convenient methods well-known in the art may be used to eliminate the iron and zinc, provided they do not remove the copper. lead and tin in sufficient quantities to render the process uneconomical. In any event the material, either purified or in its origiof phenol, benzol (benzene), toluol (toluene), the

nal state, is cast into anodes when it consists essentially of copper, lead and tin.

An electrolyte is made up containing water, copper sulphate, free sulphuric acid and a smaller amount of an aromatic sulphonic acid whose lead salt is soluble. The electrolyte preferably contains more free sulphuric acid and total sulphate radical than is present in the straight sulphuric acid baths previously employed to refine copper-bearing materials of the type with which this invention is intended to be used. The copper-bearing material to be refined is cast into anodes which are suspended in the electrolyte and an electric current is caused to flow from the anodes through the bath to suitablecathodes, such as copper'sheets, whereby pure copper is deposited at the cathodes and the other constituents of the anodes are either retained in solution or suspension in the electrolyte or are found in the anode slimes.

Among the aromatic sulphonic acids which may be added to the copper sulphate-sulphuric acid bath are the mono and poly sulphonic acids cresols, the xylenes, the xylenols, naphthaline, the naphthols, anthracene; phenanthrene and related compounds. The related chloro and nitro sulphonic acids of these aromatic hydrocarbons may likewise be used.

The aromatic sulphonic acids are used in the electrolyte for several reasons. In the first place, they dissolve not only copper, but also lead and tin. In addition, they have a high conductivity, they are relatively non-volatile and are not appreciably decomposed electrolytically. high conductivity results in low power consumption and their stability makes them economical to use because they can be recovered and reused. The lead salts of these acids are water soluble, at least in warm solutions, and the presence of one or more of these acids in suitable quantity in the electrolyte greatly improves the anode corrosion, tends to lower the operating voltage of the bath and increases the over-all eiiiciency on the electrolytic refining process.

Example I In carrying out one specific process embodying the invention, anodes are cast of copper-bearing materials consisting of about 86% copper, 6% tin, 7% lead, 1% zinc and less than 0.25% antimony, less than 0.1% iron and less than 0.4% nickel. These anodes are then electrolyzed in an electrolytic cell comprising an aqueous electrolyte containing about 30 grams per litre of copper, principally in the form of copper sulphate, about grams per litre of free sulphuric acid and about v60 grams per litre of benzene disulphonic acid, the cathodes being thin sheets of electrolytic copper. other similar agent is also added to the electrolyte to insure the production of a good copper deposit on the cathodes. The temperature of the bath is maintained at about 50 C., a cathode current density of about 15 amperes per square foot is employed and the average voltage of the cell is about 0.24 volt.

As the anodes are consumed, fresh ones are supplied, and when the cathodes have received a sufllcient deposit of pure copper they are replaced by newones. The electrolytic copper produced may be melted and cast into wire bars or other shapes, it may be used as a constituent of bronze or applied to any other purpose for which electrolytic copper of high purity is suitable.

Their A small amount of glue or.

per.

Since the constituents of the, anode otherthan the copper will either be precipitated in the form of anode slimes or will remain dissolved or suspended in the electrolyte, it is evident that more copper will deposit at the cathodes than will be dissolved at the anodes. In order to maintain the copper concentration of the bath at the desired value, this deficiency is made up by dissolving copper externally of the electrolytic cell. This is preferably accomplished by circulating a portion of the electrolyte through oxidizer tanks containing particles of pure copper or relatively pure copper scrap in a finely divided form. Usually air is'blown through the electrolyte in the oxidizer tanks to render the copper more soluble.

In view of the fact that only copper is deposited at the cathode, theconcentration of those constituents of the anode which are soluble in the taken to avoid this condition. Consequently, a

portion of the solution is removed from time to time and the copper contained therein is removed by electrolyzing the solution, using an insoluble anode of a type well-known in the art, until the bulk of the copper is removed. The remaining solution is then electrolyzed, also with an insoluble anode, to precipitate the remainder of the copper together with any tin that is dissolved in the electrolyte. If desired, the copper may be removed from-the solution by cementation with tin, and the tin then removed by electrolysis.

After the removal of the copper and the tin, the electrolyte is concentrated to a point where the salts of such metals as zinc, iron and nickel contained therein are crystallized out and the resulting strong acid is reused to make up fresh electrolyte. If desired, the salts which are crystallized out may be worked up by any suitable method to separate the constituent metals and to regenerate the acids used in the electrolyte.

The anode slimes which are produced are also treated to recover the valuable metals found therein. These slimes usually contain precious" metals and also contain, in the form of lead sulphate, all of the lead obtained from the anodes and substantially all of the tin and antimony originally in the anodes, together with some cop- A typical analysis showed the following amounts of the latter metals to be present in the slimes: 12% copper, 24% tin, 29% lead and 1.6% antimony. Any suitable process may be employed to purifythese slimes, but one which has been proved to be satisfactory comprises roasting the slimes and leaching the roasted material with sulphuric acid to dissolve out the copper as copper sulphate. The leaching acid containing the dissolved copper sulphate may then be employed to make up fresh electrolyte. The leached residue is roasted with sodium carbonate and leached with water to remove the soluble sodium sulphate produced. The remaining material is smelted in the, usual manner to produce a composite metal consisting substantially of lead, tin and antimony, which may be used in that form or may be further refined if desired.

If the-precious metals found in the slimes are of sufilcient value to warrant their recovery, they may be recovered from the slimes by any suitable process known to the art.

The concentrations of the various ingredients of the electrolyte may be varied considerably without impairing the usefulness of the process. For example, the free sulphuric acid may range from about 50 grams per litre to about 200 grams.

per litre or more, although it ispreferred to use at least 100 grams per litre of free sulphuric acid. The benzene disulphonic acid may vary from about 15 grams per litre to about 200 grams per litre or more depending upon the sulphuric acid content of the bath and upon the composition of the anodes, particularly the amount of lead in the anodes. However, it is uneconomical to employ more benzene disulphonic acid than is required to obtain the desired results because at present this acid is comparatively expensive. Usually at least 30 grams per litre and not more than about l00 grams-per litre oi-benzene disulphonic acid are required for the concentrations of sulphuric acid mentioned and with anodes of about the lead contents referred to hereinabove. The copper concentration of the bath may likewise be varied, if desired, and the temperature, current density and voltage of the cell likewise may be changed to suit varying conditions.

By purifying copper-bearing materials of the type described in accordance with the foregoing process, substantially all of the difiiculties encountered in processes of the prior art are eliminated. The corrosion of the anodes is entirely satisfactory, the voltage of the cell is such that the process may be conducted economically and the cathode current efiiciency is excellent. The anode slimes instead of forming a hard layer uponthe anodes, as is customary in the processes formerly known, gradually slufi ofi of the anodes and fall to the bottom of the cell. Consequently, the anodes may be used until they are substantially "all dissolved, whereas formerly'the anodes had to be scraped frequently to remove the accumulated slimes and considerable portions of the anodes had to be reworked and recast into anodes. When it is realized that the sulphuric acid baths formerly employed to refine copper-bearing materials of this kind operate at about 0.6 volt and in accordance with the improved process the average voltage is only about 0.25 volt, the savings in large scale operations will be immediately apparent,

Ezvomple I! In accordance with another specific embodiment of the invention, anodes of the type employed in the process of Example I are electrolyzed in an electrolytic cell containing substantially the same electrolyte as is described in ard in the operating conditions of the elec-' trolytic cell. The free sulphuric acid present in the bath may vary from about 50 grams per litre to about 200 grams per litre. The amount of phenol sulphonic acid employed may vary con- .siderably in accordance with the amount of free sulphuric acid in the'bath and the composition of the anodes, and maybe as low as 15 grams per litre. When refining anodes of the type described in electrolytes such as 'are referred to hereinabove, the concentration of the phenol sulphonicacid should notibe less than about 40 grams per litre. More than grams per litre thereof may be employed, if desired. While greater quantities of phenol sulphonic' acid will do no harm, it is uneconomical to employ more phenol sulphonic acid than is required because of the present relatively high cost of this material. Usually it is not necessary to employ more than about 100 grams per litre of phenol sulphonic acid in sulphuric acid electrolytes of the concentrations described and with the types of anodes mentioned, but up to about 200 grams per litre or more thereof may be used with satisfactory results.

The inclusion of phenol sulphonic acid in copper sulphate-sulphuric acid electrolytes of the concentrations described assists materially in maintaining satisfactory corrosion of the anodes and permits the process to operate satisfactorily at a low voltage.

Instead of the benzene disulphonic acid and phenol sulphonic acid employed in the foregoing specific examples, the other aromatic 'sulphonic acids referred to hereinabove may be employed as long as they are present in suflicient quantity results in such substantial improvements has not been definitely determined. While it is not de-' sired that the invention be limited to any particular theory, it appears that the eifect of employing a certain quantity of an aromatic sulphonic acid constituent is to cause a momentary solution of at least a considerable part of the lead contained in the anodes, which is followed by a, reaction of the resulting soluble lead salt with the sulphuric acid to form insoluble lead sulphate. However, instead of the lead sulphate being formed directly upon the anodes, asis the case when no aromatic sulphonic acid is included, it appears that the lead sulphate is formed at a point sufficiently distant from the anodes to permit the precipitated lead sulphate to fall to the bottom of the cell rather than to to achieve the desired corrosion of the anodes and to improve the efliciency of the process.

' The reference herein to the use of specific acids I such as benzene disulphonic acid or phenol sul phonic acid, to the copper sulphate-sulphuric acid electrolyte, it is also within the purview of the invention to add to such an electrolyte a suflicient quantity of one or more salts of such acids which will react with the sulphuric acid present in the electrolyte to form the desired aromatic sulphonic acid or acids. 1e salts 1 used for this purpose must necessarily be ones which will not interfere with the normal operation of the electrolytic cell and will not contaminate the anode slimes. Preferably they are salts of one or more of the metals already present in the bath. Thus instead of benzene d".-

materials.

sulphonic acid, one may use one or more of the .sulphonic acid constituents to inhibit polarization of anodes of copper-bearing materials, or words of similar import. it is intended to include the use of either the aromatic sulphonic acids themselves or of salts thereof. Likewise, the salts of aromatic sulphonic acids referred to herein and in the annexed claims are intended to include only those salts that do not introduce undesirable constituents into the electrolyte or into the anode slimes.

The reason why the addition of aromatic sulphonic acids to these sulphuric acid electrolytes deposit upon the anodes. Consequently, the

is materially less than would be the case in the absence of the aromatic sulphonic acid, the corrosion of the anodes is greatly accelerated and the resistance of the cell is greatly reduced.

The addition of these aromatic sulphonic acids also permits the use of considerably higher concentrations of sulphuric acid than have previously been employed in processes of this nature and with their use baths containing considerably more than 100 grams per litre of free sulphuric acid may be employed with entirely satisfactory results. The use of high concentrations of free sulphuric acid in the electrolyte assists in lowering the resistance of the electrolytic cell and improves the efliciency of the process.

From the foregoing description it is apparent that the invention provides simple, eflective and economical processes for refining copper-bearing It' also provides new and improved electrolytes and electrolytic processes for the separation of metals, including copper, lead and tin. Since various modifications and changes may be made to adapt the invention to varying conditions, the invention is not limited to the specific embodiments described herein but embraces all modifications and equivalents falling within the scope of the annexed claims.

Whenever the term copper-bearing materials is employed herein and in the annexed claims, it is intended to mean such materials which contain more than 50% of copper and which are substantially free of non-metallic impurities.

What is claimed is:

l. The process of refining lead-containing materials consisting principally of copper, which comprises electrolyzing anodes of such a material in an electrolytic cell comprising an aqueous copper sulphate electrolyte containing at least 100 but not substantially more than 200 grams per litre of free sulphuric acid and also containing suflicient material from the class consisting of aromatic sulphonic acids to materially inhibit polarization of the anodes.

2. The process of refining lead-containing ma terials consisting principally of copper, which comprises electrolyzing anodes of such a material in an electrolytic cell comprising an aqueous cop- 'per sulphate electrolyte containing at least but not substantially more than about 200 grams per litre of free sulphuric acid and at least 15 grams per litre of benzene disulphonic acid.

3. The process of refining lead-containing materials consisting principally of copper, which comprises electrolyzing anodes of such a material in an aqueous electrolytic cell comprising a copper sulphate electrolyte containing about 150 grams per litre of free sulphuric acid and also containing sufiicient material of the class consisting of aromatic sulphonic acids to substantially inhibit polarization ofthe anodes, where- 4. The process of refining lead-containing materials consisting principally of copper, which comprises electrolyzing anodes of such a material in an electrolytic cell comprising an aqueous copper sulphate electrolyte containing about 150 grams per litre of free sulphuric acid and at least 30 grams per litre of benzene disulphonic acid.

.5. The process of refining lead-containing materials consisting principally of copper, which comprises electrolyzing anodes of such a material in an aqueous electrolytic cell comprising a copper sulphate electrolyte containing materially in excess of 50 but not substantially more than about 200 grams per litre of free sulphuric acid v and at least 15 grams per litre. of phenol sul-- phonic acid.

6. The process oi refining lead-containing 'materials consisting principally 'of copper, which comprises electrolyzing anodes of such material in an electrolytic cell in which the electrolyte is an aqueous solution containing about grams per litre of copper in the form of copper sulphate.

but not substantially more than about 200 grams per liter of free sulphuric acid and also containing a sufilcient quantity of material from the class consisting of benzene disulphonic acid and phenol sulphonic acid to materially inhibit polarization of theano'des,

8. The process of refining metallic materials consisting principally of copper and containing minor quantities of lead, which comprises electrolyzlrm anodes of such a material in an electrolytic cell comprising an aqueous copper sulphatesulphuric acid electrolyte containing at least 50 but not substantially more than about 200 grams per liter of free sulphuric acid and also containing sufi'icient material from the class consistin of aromatic sulphonic acids to materially inhibit polarization of the anodes.-

9. The process oi refining materials consisting principally of copper and containing minor quantitles of lead, which comprises electrolyzing anodes of such a material in an electrolytic cell comprising an aqueous copper sulphate-sulphuric cient benzene disulphonic acid to maintain free corrosion of the anodes.

10. The process of refining materials consisting principally of copper and containing minor quantitles of lead, which comprises electrolyzing anodes of 'such a material in an electrolytic cell comprising an aqueous copper sulphate-sulphuric acid electrolyte containing at least but not substantially more than about 200 grams per liter of free sulphuric acid and also containin sufficient phenol sulphonic acid to maintain free corrosion p! the anodes.

11. The process of refining lead-containing materials consisting principally of copper, which comprises electrolyzing anodes of such a material ir f an electrolytic cell comprising an aqueous copper sulphate electrolyte containing in excess of 50 but not substantially more than about 200 grams per liter of free sulphuric acid and from about 15 to about 200 grams per liter of benzene disulphonic acid.

12. The, process of refining lead-containing materials consisting principally of copper, which comprises electrolyzing anodes of such a material in an electrolytic cell comprising an aqueous copper sulphate electrolyte containing at least about 100 but not substantially more than about 200 grams per liter of free sulphuric acid and from about 30 to about 100 grams per liter of benzene disulphonic acid.

13. The process or refining lead-containing materials consisting principally of copper, which comprises electrolyzing anodes of such a material in an electrolytic cell comprising an aqueous copper sulphate electrolyte containing in excess of 50 but not substantially more than about 200 grams per liter of iree sulphuric acid and from about 15 to about 200 grams per liter of phenol sulphonic acid.

14. The process of refining lead-containing materials consisting principally of. copper, which comprises electrolyzing anodes of such a material in an electrolytic cell comprising an aqueous copper sulphate electrolyte containing at least about 100 but not substantially more than about 200 grams per liter of free sulphuric acid and from about 40 to about 100 grams per liter of phenol sulphonic acid.

- 15. The process 01' refining lead-containing materials consisting principally of copper, which comprises electrolyzing anodes of such a material in an electrolytic cell comprising an aqueous copper sulphate electrolyte containing about 150 grams per liter of free sulphuric acid and at least acid electrolyte containing at least 50 but not I substantially more than about 200 grams per liter 01' free sulphuric acid and also containing sum- 40 grams per liter of phenol sulphonic acid.

16. The process 'of refining lead-containing materials consistingprincipally of copper, which comprises electrolyzing anodes of such material in an electrolytic cell in which .the electrolyte is an aqueous solution containing about 30 grams per liter of copper in the form of copper sulphate, about 150 grams per liter of free sulphuric acid, and about grams per liter oi'phenol sulphonic acid.

SIDNEY A. CORREN. v 

